Fiber optic cable thermal protection device and method

ABSTRACT

A thermal protection device for a fiber optic cable includes a loop formed on the cable and a plurality of sub-units within the cable removed from an outer jacket. A circumferential cut is made through an outer jacket of each sub-unit. A tube is placed about the cut in each sub-unit. A carrier is positioned about each of the tubes and each sub-unit including a circumferential cut. A fiber optic system includes a thermal protection device for sub-units of a fiber optic cable within a frame. A method of providing thermal protection for a fiber optic cable. A kit for providing thermal protection to telecommunications cables.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent Ser. No. 10/930,682filed on Aug. 31, 2004 now U.S. Pat. No. 7,221,832, entitled FIBER OPTICCABLE THERMAL PROTECTION DEVICE AND METHOD, the disclosure of which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention generally relates to devices and methods forprotecting fiber optic cables from damage or loss of performance due tochanges in temperature.

BACKGROUND

Fiber optic cables generally include a fiber optic strand and one ormore outer jackets. When the cable experiences temperature changes, oneor more of the jackets can contract or expend at a different rate fromthe inner cable members, including the fiber strand. There is a need fordevices and methods that reduce the effects of differential thermalexpansion and contraction characteristics of the fiber optic cable.

In telecommunications networks installed in the field, it is known tohave a large multi-fiber cable, such as an outside plant (OSP) cable,including multiple sub-units or cables within an outer jacket, with astrength member extending along with the sub-units. Each of thesesub-units may include one or more optical fiber strands within an outerjacket. As the larger cable is extended throughout the area to whichservice is desired, at a plurality of fiber access enclosures, fiberstrands in one or more of the sub-units with the larger cable may beextracted and spliced, or otherwise connected to a customer drop cable.The remaining sub-units within the larger cable continue on the route ofthe larger cable to be split off at a further fiber access enclosure.Those sub-units, which are passed through an enclosure with connectingto customer or other cables, are referred to as “expressed” sub-units.

Fiber access enclosures are often surface or pedestal mountedenclosures, subject to extremes of temperature due to the externalenvironmental conditions. The materials in the sub-units, such as thefiber strands, the external jackets and potentially water blocking gelwithin the jacket about the fiber strands, may all react differently toexposure to these temperature extremes. For example, the jackets maycontract more in cold temperatures than the relatively stable fiberstrands. Differential contraction of the jacket with respect to thefiber strands can cause micro-bending of the fiber strands with thesub-units, leading to unacceptable attenuation losses with the fiberstrands.

It is desirable to provide for the differential thermal expansion andcontraction characteristics of the elements of the sub-units to beaccommodated to reduce the level of attenuation induced by temperatureextremes.

SUMMARY

The present invention relates generally to a device and method toprovide thermal protection to a fiber optic cable. More specifically,the present invention relates to a fiber optic cable with a cable outerjacket and at least one sub-unit within the outer jacket. The sub-unitincludes at least one optical fiber and a sub-unit outer jacket. Atleast one sub-unit is removed from the cable outer jacket. Acircumferential cut through the sub-unit outer jacket is included in thesub-unit removed from the cable outer jacket. A tube is positioned aboutthe sub-unit extending on either side of the circumferential cut and acarrier positioned about the sub-unit on both ends of the tube.

The present invention also relates to a system for providing thermalprotection to a fiber optic cable including a frame with a cable entryand a cable exit. A fiber optic cable extends from the cable entry tothe cable exit and forms a loop. The cable includes a cable outer jacketand at least one sub-unit, and the at least one sub-unit is removed fromthe cable outer jacket along the loop. Each of the at least onesub-units includes an outer jacket and at least one optical fiber, and acircumferential cut through the outer jacket along the loop. A tubeextends along a portion of the at least one sub-unit about thecircumferential cut, and a carrier is positioned about the sub-unitabout the tube.

The present invention further relates to a method of protecting a fiberoptic cable including providing an optical fiber cable with a cableouter jacket and at least one sub-unit, each sub-unit including an outerjacket and at least one optical fiber. The optical fiber cable isextended into a loop. At least one sub-unit is removed from the cableouter jacket along the loop. A circumferential cut is made through theouter jacket of the at least one sub-unit along the loop. A tube ispositioned about the at least one sub-unit over the circumferential cut,and the sub-unit and the tube about the sub-unit are placed within acarrier.

The present invention relates still further to a kit for providingthermal protection to a telecommunications cable including a carrier anda plurality of tubes. The carrier includes a base with opposingendplates. The endplates each include a plurality of slots for receivingthe telecommunications cable. The tubes include a split from one end toan opposite end and are sized to be received about thetelecommunications cable and between the endplates of the carrier.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate several aspects of the presentinvention and together with the description, serve to explain theprinciples of the invention. A brief description of the drawings is asfollows:

FIG. 1 is a perspective view of a frame for mounting fiber opticequipment within a fiber enclosure.

FIG. 2 is a cross-sectional view of a multi-strand fiber opticdistribution cable.

FIG. 3 is a cross-sectional view of a fiber optic sub-unit within thefiber optic distribution cable of FIG. 2.

FIG. 4 is a closer view of a thermal protection device mounted withinthe frame of FIG. 1, with sub-units of a fiber optic distribution cableextending through the device.

FIG. 5 is a tube for use with the thermal protection device of FIG. 4.

FIG. 6 is a partial cross-sectional side view of one of the sub-units ofFIG. 3, with a portion of the tube removed.

FIG. 7 is a perspective view of a carrier of the protective device ofFIG. 4.

FIG. 8 is an end view of the carrier of FIG. 7.

FIG. 9 is a side view of the carrier of FIG. 7.

FIG. 10 is a top view of the carrier of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the exemplary aspects of thepresent invention that are illustrated in the accompanying drawings.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

Fiber optic distribution and access termination enclosures are wellknown and provide an environmentally protected field installation toconnect distribution optical fibers with customer drop cables. Insidethese enclosures are typically frames to which different pieces ofequipment for routing, splicing and connecting cables. FIG. 1 shows aframe 10 which may be mounted to a base 11 positioned in ground 9 andalso mounted within an enclosure 7, shown schematically in FIG. 1. Amulti-strand optical fiber distribution cable 12 passes through a firstcable access 14 and a second cable access 16 for routing through severalcable routing features 34 of frame 10. Adjacent first cable access 14 isa first cable clamp 18, and adjacent second cable access 16 is a secondcable clamp 20. Each of the cable clamps 18 and 20 include a strengthmember clamp 22 and an outer jacket clamp 24 and provide a secure anchorfor cable 12 at its entry and exit from frame 10.

Cable 12 includes an outer jacket 26 and a plurality of sub-units 28(additional details of cable 12 are described below in FIGS. 2 and 3).Sub-units 28 are broken out from outer jacket 26 and a loop 32 ofsub-units 28 extends between cable clamps 18 and 20. Adjacent each cableclamp 18 and 20 is a cable thermal expansion protection device 30.Another device 30 is positioned along loop 32 at approximately themid-point of the loop. Within frame 10, one or more of the sub-units 28may be split out of cable 12 above cable clamp 18 to be spliced orconnected to customer drop cables, or to branch out from the enclosureto service customers who are not conveniently located to cable 12. Theremaining sub-units 28 are passed or expressed through cable clamp 20and out cable access 16, to transit to other enclosures or equipmentfurther downstream in the network. Loop 32 includes those expressedsub-units 28.

FIG. 2 shows a cross-section of cable 12, with outer jacket 26 aboutsub-units 28. Cable 12 is shown as an outside plant (OSP) cable althoughother types and styles of multi-strand optical fiber cables may also beused. A central strength member 36 extends through cable 12. To extendcable 12 through frame 10, cable 12 may be clamped at outer jacket clamp24 of one of the cable clamps 18 or 20. A sufficient length of cable 12is drawn up to form the desired length of loop 32 and cable 12 isclamped at outer jacket clamp 24 of the other cable clamp. Outer jacket26 of cable 12 is removed between outer jacket clamps 24 to exposesub-units 28 and central strength member 36. Strength member 36 may beextended to and clamped by each of the strength member clamps 22 andtrimmed so that it does not extend along loop 32. Any sub-units 28 beingsplit out for splicing, connecting or branching within frame 10 are alsoremoved from loop 32 and the remaining sub-units 28 are the expressedsub-units.

Frame 10 and the enclosure in which it is mounted may be installed at alocation exposed to the environment, including temperature extremes.Within each sub-unit 28, as shown in FIG. 3, may be an outer jacket 38and a plurality of sheathed optical fibers 40. Filling the space aboutfibers 40 may be a water blocking gel to prevent water infiltration andmigration within sub-unit 28. Fibers 40 and outer jacket 38 may havedifferent coefficients of thermal expansion, so that each will elongateor contract different amounts in response to the temperature extremes.Fibers 40 may typically be more thermally stable than jacket 38. Thus,to accommodate elongation of jacket 38, fibers 40 are loosely andslidably positioned within sub-unit 28. This may provide enough excessfiber length to account for the additional elongation of jacket 38without excessively tensioning fibers 40. However, when jacket 38contracts, the excess fiber length within sub-unit 28 is increased tothe extent that micro-bending may occur, resulting in undesirable andpotentially unacceptable attenuation losses to signals transmittedthrough the fiber.

Cable thermal protection device 30 permits the differential in thermalexpansion and contraction of the elements of sub-units 28 to becompensated for to avoid excessive attenuation losses within fibers 40.Device 30 includes a carrier 44 through which the expressed sub-unitsextend through and each of the expressed sub-units is sheathed in a tube46 within carrier 44. Carrier 44 includes a pair of opposing endplates48 and 50 between which tubes 46 are captured. Carrier 44 also includesa base 52 that is mounted adjacent frame 10. A strap connector such astie-wrap 54 extends about tubes 46 and sub-units 28, and through a loop56 formed in base 52 to hold sub-units 28 and tubes 46 between endplates48 and 50.

Tube 46 is illustrated in FIG. 5, and may include a split 58 extendingthe length of tube 46. At one end of tube 46, a chamfer 60 is formed oneither side of split 58 to ease entry of sub-unit 28 into tube 46.

FIG. 6 shows tube 46 with an expressed sub-unit 28. Within tube 46, acircumferential or ring cut 62 is made through outer jacket 38 ofexpressed sub-unit 28, creating two intermediate ends 64 and 66 of outerjacket 38 on either side of ring cut 62. This circumferential cut may bemade with known products, such as the Cable Stripper, part number45-463, made by IDEAL, and utilizing existing field practices. The cutdoes not extend through any portion of fiber 40. As fiber 40 is slidablewithin outer jacket 38, the cut permits outer jacket 38 and fibers 40 tocontract independent of each other. As shown in FIG. 6, outer jacket 38has contracted, pulling intermediate ends 64 and 66 away from eachother. Fibers 40, which contract less, are free to slide within outerjacket 38 and leave a portion of fibers 40 exposed between theintermediate ends. This allows outer jacket 38 to contract in responseto environmental conditions without causing undesirable attenuationwithin fibers 40. Where outer jacket 38 has pulled back along cut 62,fibers 40 are left without protection from flexing or damage that isnormally provided by outer jacket 38. This exposure may leave fiberssusceptible to damage or unacceptably sharp bends. Tube 46 extends alongouter jacket 38 across cut 62 to provide the support to fibers 40exposed by cut 62.

It is also known that some materials used to make outer jacket 38 willadopt a permanent set, or contracted length, after repeated exposure totemperature changes. Cut 62 allows these permanent sets to becompensated for as well. Cut 62 will also expose water blocking gel 42within each sub-unit 28, potentially allowing the gel to escape fromouter jacket 38. A close fit between tube 46 and outer jacket 38 mayserve to reduce the amount of leakage of gel 42. However, as loop 32 isformed in a sealed enclosure within which frame 10 is mounted, so thatthe chance of water infiltration is relatively minor and the escape of aportion of gel 42 is acceptable.

Several devices 30 may be mounted along loop 32 within frame 10,although the number of devices required may vary with the length andthermal characteristics of loop 32. Loop 32 may be short enough, or thedifference in thermal coefficients of expansion may be small enough thatonly a single device 30 is required. Added length of loop 32, or greaterdifferences in the thermal coefficients of expansion of outer jacket 38and fibers 40 may call for additional devices 30 along loop 32.

Loop 32 is preferably sized so that loop 32 can by folded back on itselfto lie within frame 10 so that an enclosure can be positioned aboutframe 10. In such a folded over configuration, the mid-loop mounteddevice 30 would lie adjacent one of the lower mounted cable routingfeatures 34 on frame 10. It is anticipated that a ribbon cable or otherforms of multi-strand fiber optic distribution cables may used with thethermal protection device shown herein.

FIGS. 7 to 10 show carrier 44 with endplates 48 and 50 and base 52.Endplates 48 and 50 each include a plurality of slots 68 for receivingsub-units 28. Slots 68 are deep enough to hold at least one sub-unit 28,and may be configured to hold more than one, depending on the number ofsub-units being expressed through a particular frame 10. Slots 68 arealso narrow enough to prevent passage of tube 46 along the length of anyof the sub-units 28 within a slot 68. This will prevent any unwantedsliding or migration of tubes 46 from about cuts 62 in sub-units 28.Each slot 68 may include one or a pair of tapered entries 70 to aid inthe positioning of sub-units within the slot. However, it may desirablefor slots 68 to be configured with a uniform width, for example, ifslots 68 are configured to hold two sub-units, or if endplates 48 and 50were made smaller and the overall depth of any slot 68 was closer to thesize of a sub-unit, or for other reasons. Loop 56 in base 52 defines anopening 72 to receive tie-wrap 54 or some other form of holddown orstrap connector to secure sub-units to device 30. A pair of fasteneropenings 74 is included in base 52 to aid in mounting of device 30 toframe 10. It is also anticipated that an adhesive may be used to mountdevice 30.

Referring now to FIGS. 5 and 9, carrier 44 defines a width W betweenendplates 48 and 50. This width W is preferably closely matched andslightly greater than a length L of tube 46. Length L should besufficiently long to cover any expected separation between intermediateends 64 and 66 and extend from cut 62 along a portion of outer jacket 38adjacent cut 62 to provide the desired support to any exposed fibers 40of sub-unit 28. This desired length L may change due to the thermalcharacteristics of sub-units 28 and length of loop 32 but may not exceedwidth W. When the desired length L approaches width W, an additionalthermal protective device 30 should be included in loop 32. For theanticipated length of loop 32 shown and described above, it isanticipated that three devices 30 will be desirable to provide adequatethermal and other protection to the fibers within sub-units 28. It isanticipated that the device 30 positioned mid-loop along loop 32 willnot be fastened or mounted to frame 10 but will be attached only tosub-units 28, providing improved future access to frame 10 as loop 32can be moved away from frame 10, as shown in FIG. 1.

The embodiments of the inventions disclosed herein have been discussedfor the purpose of familiarizing the reader with novel aspects of thepresent invention. Although preferred embodiments have been shown anddescribed, many changes, modifications, and substitutions may be made byone having skill in the art without unnecessarily departing from thespirit and scope of the present invention. Having described preferredaspects and embodiments of the present invention, modifications andequivalents of the disclosed concepts may readily occur to one skilledin the art. However, it is intended that such modifications andequivalents be included within the scope of the claims which areappended hereto.

1. A method of protecting an optical fiber cable comprising: providingan optical fiber cable with a cable outer jacket and at least onesub-unit, each sub-unit including an outer jacket and at least oneoptical fiber; removing the at least one sub-unit from the cable outerjacket; making a circumferential cut through the outer jacket of the atleast one sub-unit without damaging the optical fiber; positioning atube about the at least one sub-unit over the circumferential cut,wherein the optical fiber of the at least one sub-unit is a continuous,unbroken, unspliced optical fiber within the tube; and placing the atleast one sub-unit and the tube about the sub-unit within a carrier. 2.The method of claim 1, further comprising tying the sub-units and thetubes about the sub-units to the carrier.
 3. The method of claim 1,further comprising mounting the carrier to a frame.
 4. The method ofclaim 1, further comprising making a circumferential cut through theouter jacket of a plurality of sub-units, positioning a tube over thecircumferential cut in each of the plurality of sub-units, andpositioning each of the plurality of tubes and sub-units within thecarrier.
 5. The method of claim 4, further comprising extending theoptical fiber cable into a loop, and removing the at least one sub-unitfrom the cable outer jacket along the loop.
 6. A fiber optic cablecomprising: a cable outer jacket and at least one sub-unit, the at leastone sub-unit including at least one optical fiber and a sub-unit outerjacket; at least one sub-unit removed from the cable outer jacket; thesub-unit removed from the cable outer jacket including a circumferentialcut that extends through the sub-unit outer jacket and not the opticalfiber; a tube positioned about the sub-unit extending on either side ofthe circumferential cut, wherein the optical fiber of the at least onesub-unit is a continuous, unbroken, unspliced optical fiber within thetube; and a carrier positioned about the sub-unit on both ends of thetube.
 7. The fiber optic cable of claim 6, further comprising alongitudinally extending strength member within the cable outer jacket.8. The fiber optic cable of claim 6, wherein the tube includes alongitudinally extending split extending from one end of the tube to anopposite end of the tube.
 9. The fiber optic cable of claim 8, whereinthe split in the tube adjacent one end of the tube includes a chamferedopening to the split.
 10. The fiber optic cable of claim 6, wherein thecarrier includes a pair of opposing endplates, each endplate including aplurality of slots sized to receive one of the at least one sub-units.11. The fiber optic cable of claim 10, wherein the endplates of thecarrier are spaced apart a width greater than a length of the tube, theat least one sub-unit is positioned within one of the slots of eachendplate, and the tube is positioned about the sub-unit between theendplates of the carrier.
 12. The fiber optic cable of claim 6, whereinthe cable is formed into a loop, the cable outer jacket is removed fromthe sub-units along the loop and the at least one sub-unit extends alongthe loop, and the at least one sub-unit includes a plurality ofcircumferential cuts, with a tube mounted about each cut and a carriermounted about each tube.
 13. The fiber optic cable of claim 12, furthercomprising a longitudinally extending strength member along which the atleast one sub-unit extends within the cable outer jacket, wherein thestrength member has been removed along the loop.
 14. The fiber opticcable of claim 6, wherein the cable includes a plurality of sub-units.15. The fiber optic cable of claim 14, wherein a plurality of sub-unitsis removed from the cable outer jacket, each sub-units including acircumferential cut, a tube positioned about the sub-unit about the cutand a carrier positioned about the sub-unit on either end of the tube.16. The fiber optic cable of claim 15, wherein each tube includes alongitudinally extending split extending from one end of the tube to anopposite end of the tube.
 17. The fiber optic cable of claim 16, whereinthe split in the tube adjacent one end of the tube includes a chamferedopening to the split.
 18. The fiber optic cable of claim 14, wherein thecarrier includes a pair of opposing endplates, each endplate including aplurality of slots sized to receive the plurality of sub-units.
 19. Thefiber optic cable of claim 18, wherein the endplates of the carrier arespaced apart a width greater than a length of the tube, each of theplurality of sub-units is positioned within one of the slots of eachendplate, and one of the tubes is positioned about each sub-unit betweenthe endplates of the carrier.
 20. The fiber optic cable of claim 14,wherein the cable is formed into a loop, the cable outer jacket isremoved from the sub-units along the loop and the plurality of sub-unitsextend along the loop, and each sub-unit along the loop includes aplurality of circumferential cuts, with a tube mounted about each cutand a carrier mounted about each tube.
 21. The fiber optic cable ofclaim 20, further comprising a longitudinally extending strength memberalong which the plurality of sub-units extend within the cable outerjacket, wherein the strength member has been removed along the loop. 22.The fiber optic cable of claim 14, further comprising a longitudinallyextending strength member within the cable outer jacket.
 23. A fiberoptic cable comprising: a cable outer jacket and at least one sub-unit,the at least one sub-unit including at least one optical fiber and asub-unit outer jacket; at least one sub-unit removed from the cableouter jacket; the sub-unit removed from the cable outer jacket includinga circumferential cut that extends through the sub-unit outer jacket andnot the optical fiber; a tube positioned about the sub-unit extending oneither side of the circumferential cut, wherein the optical fiber of theat least one sub-unit is a continuous, unbroken, unspliced optical fiberwithin the tube; a carrier positioned about the sub-unit on both ends ofthe tube; wherein the cable includes a plurality of sub-units, andwherein the cable is formed into a loop, the cable outer jacket isremoved from the sub-units along the loop and the plurality of sub-unitsextend along the loop, and each sub-unit along the loop includes aplurality of circumferential cuts, with a tube mounted about each cutand a carrier mounted about each tube; and a longitudinally extendingstrength member along which the plurality of sub-units extend within thecable outer jacket, wherein the strength member has been removed alongthe loop.